Presently, in the 3GPP (Third Generation Partnership Project), the standardization of LTE-advanced (hereinafter the LTE Release 10 specifications and the specifications of later versions will be collectively referred to as “LTE-A”), which is an evolved radio interface of the LTE (Long Term Evolution) Release 8 specifications (hereinafter referred to as “LTE” or “Rel. 8”), is in progress. LTE-A is attempting to realize higher system performance than LTE, while maintaining backward compatibility with LTE.
In the uplink of the LTE system, SC-FDMA (Single-Carrier Frequency Division Multiple Access), which realizes a low peak-to-average power ratio (PAPR) and which is effective to expand coverage, is employed. With this method, radio resources of a given frequency and time are allocated to one user terminal (UE: User Equipment) according to scheduling by a radio base station apparatus (eNB: evolved NodeB), so that user terminals in the same cell do not interfere with each other. However, the LTE system is based on one-cell frequency reuse, which uses the same frequency in all cells, and therefore the interference level from user terminals that are located on cell edges in surrounding cells is particularly high. Consequently, to compensate for such interference from surrounding cells and maintain certain received quality, measures against inter-cell interference become necessary.
To measure against inter-cell interference, the uplink transmission power control plays a significant role. A radio base station apparatus is required to control the transmission power of a user terminal to fulfill the required received quality, taking into account the propagation loss between the user terminal and the radio base station apparatus, and interference to be given against surrounding cells. In the LTE system, fractional transmission power control is employed as a transmission power control method to take inter-cell interference into account.
In the uplink of the LTE system (the PUSCH (Physical Uplink Shared Channel), the PUCCH (Physical Uplink Control Channel), and the SRS (Sounding Reference Signal)), transmission power is controlled by combining an open loop control and a closed loop control. The open loop control is executed using parameters which a radio base station apparatus reports in a comparatively long cycle, and the propagation loss measured by a user terminal. The closed loop control is executed using TPC commands which a radio base station apparatus reports in a comparatively short cycle, based on the conditions of communication (for example, the received SINR (Signal to Interference plus Noise Ratio) at the radio base station apparatus) between the radio base station apparatus and the user terminal.
For example, the transmission power of the PUSCH is controlled according to following equation 1 (non-patent literature 1). In following equation 1, i is an index to represent a subframe, j is an index to represent the scheduling type, PCMAX,C(i) is the maximum possible transmission power of a user terminal, MPUSCH,C(i) is the frequency bandwidth that is used, PO_PUSCH,C(j) is the basic transmission power of the PUSCH, PLC is the propagation loss, αC(j) is a propagation loss coefficient, ΔTF,C(j) is the amount of offset per format that is used, and fC(i) is the amount of offset based on TPC commands.
                              [                      Formula            ⁢                                                  ⁢            1                    ]                ⁢                                                                                                            P                          PUSCH              ,              c                                ⁡                      (            i            )                          =                  min          ⁢                      {                                                            P                                      CMAX                    ,                    c                                                  ⁡                                  (                  i                  )                                            ,                                                10                  ⁢                                                            log                      10                                        ⁡                                          (                                                                        M                                                      PUSCH                            ,                            c                                                                          ⁡                                                  (                          i                          )                                                                    )                                                                      +                                                      P                                                                  O                        ⁢                                                                                                  ⁢                        _                        ⁢                                                                                                  ⁢                        PUSCH                                            ,                      c                                                        ⁡                                      (                    j                    )                                                  +                                                                            α                      c                                        ⁡                                          (                      j                      )                                                        ·                                      PL                    c                                                  +                                                      Δ                                          TF                      ,                      c                                                        ⁡                                      (                    i                    )                                                  +                                                      f                    c                                    ⁡                                      (                    i                    )                                                                        }                                              (                  Equation          ⁢                                          ⁢          1                )            